Apparatus for testing cutting tools and the like



Dec. 31, 1940. P. A L 2,226,927

APPARATUS FOR TESTING CUTTING TOOLS AND THE LIKE Filed April 27, 1959 F6167; 6: ffa Z5.

fiTTOF/VEY WITNESS @ZZQMA Patented Dec. 31, 1940 UNITED STATES PATENT OFFICE APPARATUS FOR TESTING CUTTING TOOLS AND THE LIKE Application April 2'7, 1939, Serial No. 270,295

4 Claims.

As far as I am aware, there has been no way of determining in advance the ability of a metal cutting tool or the like to perform its intended duty with the result that tools which before being placed in service satisfactorily respond to any of the usual tests designed to determine their hardness and/ or tensile strength alone often fail much sooner than would be normally expected because they are deficient in some other quality.

Single point toolssuch as lathe and shaper tools usually consist of a relatively small piece of one of the numerous alloys now marketed under various trade names for the manufacture of cutting tools, removably secured in a holder and ground to the desired shape. Failure of such a tool to perform the duty reasonably anticipated from it is therefore a matter of small moment forthe tool can be readily reground in a short time if it gets dull before it should, or if it fails entirely a new tool can be substituted at comparatively small expense. However, multiple point or multiple edge cutters such as milling cutters are very costly and if they do not give the anticipated service before becoming dull their regrinding is an expensive and time consuming operation while if they fail prematurely the monetary loss is a heavy one, particularly with those cutters which are formed entirely of the highly expensive alloys as distinguished, for example, from cutters of the inserted blade type in which only the blades are formed therefrom and the body of the cutter from less expensive material.

Milling and other multiple point cutters are of almost innumerable styles and types in accordance with the particular work they are designed to perform, and to fulfill the requirements of modern machine shop practice must be of extreme accuracy. In their manufacture it is therefore customary to first rough-finish each cutter of the integral type' or to similarly rough-finish the blades or other cutting elements for cutters of the inserted blade type, then to heat-treat the rough-finished articles and finally grind them to the exact size and shape desired. After the heat treatment and/or after the final grinding, each cutter is normally subjected to one of the usual hardness tests, and if it does not satisfactorily respond thereto is discarded or perhaps re-heattreated, but a hardness test is not fully indicative of the ability of a cutter to properly perform the service for which it is intended since hardness alone is only one of many factors determinative of this ability.

"Consequently when similar cutters or cutter blades are manufactured in lots it is'sometimes the practice to make one more than the required number and after all have been heat-treated or even heat-treated and finally finished, to then test one of them by known methods to determine not only its hardness and tensile strength but perhaps other qualities as well on the assumption that the other cutters in the lot will have similar characteristics. However, not only do such tests involve the destruction of the tested cutter with consequent economic loss but in fact cannot be relied on with respect to the other cutters in the lot for two or more pieces of the same cutting alloy though of similar size and shape and subjected to exactly the same heat treatment will not necessarily have the same physical properties. So the fact that one cutter from a given lot satisfactorily passes hardness, tensile strength and perhaps other tests designed to indicate its ability to respond to the duty for which it is designed is no assurance that all the other cutters in the lot could pass the same test if subjected thereto or will have the desired duty-sustaining capacity.

It follows that a plurality of cutters believed by the maker to be exactly the same or as nearly similar as possible and capable of responding to certain given specifications so as to have equal work performing ability often actually present material variations in the latter factor and it is thus substantially impossible to predict with accuracy, on the basis of the results of testing methods heretofore available, the ability of any given cutter to satisfactorily perform in service.

In accordance with my invention, however, substantially any tool, cutter or like article itself may be tested, instead of merely testing one or more representatives of a group, in such a way as to obtain an accurate indication of its ability to perform its intended function, yet without impairing this ability or seriously damaging the tool; each individual tool may thus be tested and the sometimes extremely unfortunate results of reliance upon tests of a representative merely assumed to be like the tool actually to be used thereby avoided.

Furthermore, in accordance with my invention tests may be made indicating certain qualities which have not heretofore been susceptible of standardization for the reason that no adequate equipment for their accurate determination has been available.

Thus, while it has been possible to ascertain the hardness of the metal in a cutter or other article, and by pulling it or a sample piece apart to ascertain its tensile strength, I have found that cutters or the like which on the basis of results of such tests appear to be entirely suitable for normal use often unexpectedly fail through deficiency in some property, which I term toughness, and in which the hardness and tensile strength are not the sole determining factors. The term toughness as hereinafter used will thus be understood as designating this property, which is a function to some extent of both the hardness and tensile strength of the metal and is also probably somewhat affected by the structure, size and arrangement of its rain as well as other factors, any or all of which may vary in metals of the same chemical composition and in articles made therefrom which have been subjected to manufacturing processes as nearly similar as practicable.

In accordance with my invention I subject a given cutter or other article after it has been hardened, and either before or after finish grinding, to a measurable stress exerted against a small area of its surface at and adjacent an edge thereof, which edge may be specially prepared for the purposes of the test if desired, and then gradually increase the stress by known increments until a small quantity of the metal has been displaced, the factor of stress at the moment of rupture affording an extremely accurate indication of the toughness of the article While the character of the rupture or fracture produced constitutes an added indication of the nature of the metal. The result of a single test made upon the article itself therefore affords positive indication of its ability to perform its intended duty when put into actual use without appreciable impairment of its capacity therefor.

It is therefore a principal object of the invention to provide a machine for testing a cutting tool or other metal article with the aid of which the toughness of the metal forming the tool may be ascertained without serious damage to the tool itself, save perhaps when it is outstandingly inadequate for its intended purpose in which case, however, the fact it is damaged is immaterial.

A further object is to provide apparatus for testing cutting tools or other metal articles operable to subject a portion of the tool, preferably an edge formed by acute angled surfaces, to stress in a predetermined manner and under controlled conditions in such a way as to afford an accurate indication of the toughness of the metal and consequent ability of the tool to perform its intended duty.

Other objects, purposes and advantages of the invention will hereinafter more fully appear or will be understood from the following description'of the said apparatus and of one way of employing it for testing a typical cutting tool.

In said drawing Fig. 1 is a side elevation of the apparatus.

Fig. 2 is a front view thereof. Fig. 3 is a fragmentary enlarged side elevation showing the testing point forming a part of the In the several figures like characters are used to designate the same parts.

More specifically the said apparatus or testing machine comprises a generally U-shaped jaw or frame i having an enlarged base 2 which affords a stable support for the machine and for the article being tested which, for example and as shown, may be a lathe tool T or the like. During the test the tool is secured in any convenient way to the base 2 as by means of strap 3 bearing against the upper surface of the tool to hold it tightly against a suitable block 4 or other support resting on the base, studs 5 threaded into the latter, extending through the ends of strap and carrying nuts t for cooperation with the strap to clamp the tool and block firmly in place.

Of course, when another sort of tool, for example a circular milling cutter, is to be tested, other means for holding it on the base will frequently be utilized, the specific construction thereof being a matter of choice largely dictated by the particular character of the tool.

For convenience in illustration the tool T is shown in Figs. 1-4 in position for test by exertion of stress against one of its surfaces S1 which forms a cutting edge for the tool at its intersection with another surface S2, these surfaces forming an angle of approximately 67 at said edge to correspond with the usual practice in metal-cutting tools generally. The angle of 67 results from the customary positioning of cutting tools relatively to the work in such a way as to provide an angle of rake between the attacking face of the tool and the work of about 98 to a plane tangent to the surface of the work at the point of engagement of the tool and an angle of clearance of about 15 between the other face of the tool and said tangent plane. It will be understood, however, that it is usually preferable to test finished tools at some other point than at their actual cutting edges so as to avoid deformation of the latter and I may therefore first prepare the tool for test by simply grinding at some suitable place thereon two small plane surfaces intersecting at an acute angle, preferably about 67, to form an edge which for purposes of the test may be considered substantially equivalent to the actual cutting edge. That is, it can usually be safely assumed that the results of a test made at such a specially prepared point are substantially the same as would be obtained by similarly testing the tool at its actual cutting edge, so an accurate indication of the work-performing ability of the tool is obtained in accordance with my invention without the slightest marring of that edge; however, if the tool be tested at such edge itself the slight damage resulting can be readily eliminated by grinding and the cutting edge of the tool thus readily replaced in operative condition.

The testing machine also includes a plunger 8 vertically slidable in a suitable close fitting bore in the upper arm 9 of the frame I, with a testing point l0, hereafter more fully described removably secured as by a set screw H in its lower end. The plunger extends upwardly beyond the bore in the arm 9 and carries at its upper end a threaded adjusting screw l2 and lock nut l3 whereby the effective length of the plunger may be varied within limits and is prevented from dropping through the arm by an adjustable collar I4.

A steelyard or force beam !5, adapted to bear on the head of the screw l2 extends ,generally horizontally above the frame and has one of its ends pivotally secured to the latter adjacent the plunger by a pivot I6 passing through both the beam end and a yoke l1 formed on or secured to the upper jaw 9. The free end of this beam is graduated in a plurality of preferably equal linear divisions and carries a sliding weight l8 whereby the stress exerted by the beam against the head of the screw I2 and hence against the plunger may be varied and its value ascertained from the graduated scale.

For convenience in setting up the machine preparatory to making a test I usually place a block B under the beam l5 to support it out of contact with the screw I2 until the test is about to begin at which time the block is removed so the beam rests only upon the head of the screw.

The testing point I I] is made of high grade tool or alloy steel or other suitable extremely hard material or if desired may have an inserted tip made from a gem or the like and comprises a shank 20 by which it is held in the plunger 8 while its downwardly projecting end or tip is ground substantially conical, preferably in conformity with a conical surface which includes an angle of 60. At its extremity the point is desirably rabbeted or chamfered to form a surface 22 normal to its axis and an intersecting surface 23 substantially coincident with said axis, the surface 22 being preferably spaced from the extremity of the tool by a distance such that it forms a semi-circle of about .045" diameter so it is about 0.0008 square inch in area although its exact size is not of great importance provided a change in size is not permitted to confuse comparison of the results of several tests.

In carrying out a test with the aid of the mechanism just described, the tool or other article to be tested is so positioned that an edge thereof formed by faces intersecting at an acute angle, preferably about 67, is brought into substantial coincidence with the edge formed at the reentrant intersection between the surfaces 22 and 23 (Fig. 3) with the surface 22 preferably coincident with one plane surface of the tool; the surface 23 on the tip then forms an angle of about 23 with the other adjacent surface of the tool.

When the tool and testing machine have been positioned as just described with the article securely clamped to the base, the block B is removed from beneath the beam and the latter allowed to rest on the head of the plunger adjusting screw, preferably with the weight positioned toward the inner end of the graduated scale on the beam. The weight is then gradually shifted toward the outer end of the beam until the stress exerted by the point against the tool produces a rupture of the latter. The reading of the weight on the beam scale when the rupture occurs then affords an indication of the toughness of the material of which the tool is formed.

In the case of a tool made of extremely tough metal, the metal displaced from its edge by this test leaves a generally concave regularly shaped void V which at the upper face of the tool substantially conforms to face 22 of the testing point while the remainder of the void is bounded by a substantially smooth, generally oblique, particylindrical surface as indicated in the very much enlarged views Figs. 5, 6 and '7.

However, when the material is appreciably less tough the form of the fracture is extremely irregular and usually much larger, more nearly as indicated at V1 in Figs. 8, 9 and 10, in which a relatively large flake of highly irregular form and outline has been displaced, thus indicating an absence of toughness in the metal regardless of the stress exerted upon it.

It is, of course, usually essential that the tested article be capable of withstanding a given predetermined stress before yielding either in the manner indicated in Figs. 5, 6 and 7 or in that indicated in Figs. 8, 9 and 10, since in a relatively soft metal, such as one not utilized for metal-cutting tools, a fracture like that shown in Figs. 5, 6 and '7 may be produced by a relatively light stress while an alloy steel tool may withstand a much greater stress but ultimately fracture as indicated in Figs. 8, 9 and 10, showing the material, while perhaps hard enough, is too lacking in toughness to properly operate in service. Consequently, the most satisfactory milling cutters, lathe tools and the like, when tested in accordance with my invention have imparted to them fractures like that in Figs. 5, 6 and 7 at stress readings indicating adequate resistance prior to the occurrence of the fracture and I have found that the highest quality cutters of adequate toughness as shown by my testing machine may prior to rupturing be subjected to stresses equivalent to several hundred tons per square inch at an edge formed by faces intersecting at about 67 and that when rupture does ultimately occur as a result of increased stress it takes the form shown in Figs. 5, 6, and '7. And by actual experience I have proved that, for example, milling cutters of this character are far superior in actual use to those which my testing machine indicates are less tough, in spite of the fact that the usual hardness tests show little or no diiference between them or even superior properties in that respect. Thus any metal cutting tool which, when tested in accordance with my invention, exhibits a high degree of toughness, considering the character of the metal of which it is made, will perform more efficiently in service than an otherwise similar one of less toughness.

' It will be understood that the angle formed by tool surfaces at the edge to be tested may be an acute angle of any desired specific angularity although for the reasons heretofore stated I prefer to employ an angle of about 67 since the testing of an edge whose faces meet at such an angle may possibly indicate a little more accurately the behavior of the cutting edge itself in actual use than if an edge formed by faces meeting at a different angle were used for the test. Moreover, the area of the surface against which the pressure or stress is exerted in making a test may be varied as desired, although for purposes of comparison, it is usually simpler to use the same area for a plurality of tests and avoid the necessity for adjusting the readings for differences resulting from the use of mechanisms exerting the pressure over different areas in the several articles tested.

My invention therefore enables an accurate determination in advance of the capacity of a metal cutting tool or the like or in fact almost any metal article to perform under actual conditions of service, something which, as hitherto explained, the usual tests for hardness and/or tensile strength are unable to do. Thus by employing it after the tools have been heat-treated but before they are fiinish-ground the expense of the latter operation can be entirely avoided with respect to those which do not exhibit the requisite-toughness, while with equal facility the purchaser o a finished tool or cutter can test it before putting it into service and if it is found lacking in toughness can return it to the maker before its inability to perform its expected duty has been demonstrated by actual use which, so far as I am aware, has heretofore been the only way to determine the ability of a cutting tool to retain its cutting edge and resist fracture. The invention is therefore of great utility in the machine tool industry and is being employed with great success and economic advantage therein.

While I have described one machine Well adapted for testing metal-cutting tools in the manner described, it is to be understood that changes and modifications may be made in the operations incident to its use and/or in the details of construction of the machine, and that it may be employed either for testing single articles independently or for testing a series of similar articles for comparative purposes, without departing from the spirit and scope of the invention as defined in the appended claims,

Having thus described my invention, I claimand desire to protect by Letters Patent of the United States:

1. A machine for testing a tool or the like having acute angled surfaces intersecting at an edge, comprising a support for the tool, a plunger movable relatively to the support, a testing point carried by the plunger having a tool engaging circular segmental face normal to the path of movement of the plunger and means for exerting an increasing force against the plunger tending to move it along said path While said face is in overlying engagement with one of said tool surfaces adjacent said edge tothereby displace from the tool some of the metal proximate thereto.

2. A machine for testing a tool or the like having surfaces including an acute angle and intersecting in an edge, comprising a frame and a base, means for supporting thereon the tool to be tested, a plunger movable in the frame, a testing point carried thereby having a circular segmental face lying substantially normal to the axis of the plunger and engageable with one of said tool surfaces adjacent said edge and another face normal to said face intersecting its chord and forming a stop for the edge of the tool, a beam pivoted to the frame and overlying and engaging the plunger adjacent the pivot and means movable along the free end of the beam for adjustably increasing the pressure exerted thereby on the plunger and in turn that exerted on said tool surface by the circular segmental face of the testing point until the metal'of the tool contacted by said face is ultimately displaced. 7

3. A machine for testing a tool or the like having acute angled surfaces intersecting at an edge, comprising a testing point having a conical end rabbeted adjacent its tip to form a circular segmental tool-engaging face extending normal to the axis of the point and a face forming an angle With the first mentioned face and extending to the extremity of the point, a movable plunger carrying said point, means for rigidly supporting the tool With its said edge in coincidence with the vertex of said angle, and means operable to apply progressively increasing pressure to the plunger to thereby cause the toolengaging face of the point to press against a surface of the tool behind said edge and ultimately displace from the tool metal lying proximate said surface.

4. A machine for testing a tool or the like having acute angled surfaces intersecting in an edge, comprising a support for the tool, a testing point rabbeted adjacent its extremity to provide a face normal to its axis and a face at right angles thereto intersecting the first face, extending to the end of the point and adapted to form a stop for the edge of the tool when positioned for testing, a slidable plunger carrying 

